If you have a multi-meter, and know how to use it to troubleshoot DC circuits, you can trace the wiring to find the bad wiring or break.
If not, you will probably have to find someone to repair it for you.
I would start by inspecting the fuse board carefully, front and back. Don't forgot to remove all power.. unplug the shore power, and disconnect one terminal of the battery.
Doug and Patience and Shelby the mutt
2015 Crossroads Sunset Trail Reserve ST26RB
2013 Ford F-150 3.5 EcoBoost XLT Supercab 4x4